Thursday, February 14, 2013

Ball-and-pillow and flame structures in sand/siltstone on the north shore of Sunset Bay. Ball-and-pillow structures form when sediment of higher density ends up on top of sediment of lower density. Blobs of the upper material can then sink into the lower material. The lower material gets pushed up, typically in sharper, wavering, plumes, creating flame structures. In this case, they're mostly confined to what is likely a layer of siltstone running roughly through the middle of the photo, underneath a more resistant bed of sandstone. I couldn't get anything into the shot for scale, but as I remember, the bed of sandstone is about a foot thick.

There are a wonderful lot of colorful and fascinating sedimentary structures in this area, but due to the fact the park closed at 6 PM, we didn't have as much time as I'd hoped to poke around on this trip.